Firefox Adds Tracker Blocking

What Firefox changed yesterday

Firefox 63, released yesterday, adds a section called Content Blocking to its privacy settings.

In it, people can choose to block third-party tracking cookies, the kind set by known tracking companies whose code runs inside other sites' pages.

They can also stop known trackers loading at all, in every window rather than only in private ones.

Neither option is on in ordinary windows by default. People have to find the setting and choose it, and most will not, at least this year.

Mozilla has said it intends to make protections like these the default in later versions. So the setting matters less this month than the direction it points in.

Your cookies and other people's

A cookie is a small record a website stores in the browser, so it can tell the same browser apart on a later visit.

When your own site writes the record, under your domain, it is called first-party. Universal Analytics works this way: the identifier it uses to recognise returning visitors lives on your domain.

When an outside company writes it, through a script you placed on your page, it is third-party. An ad network's script sits on thousands of sites, so its record can link one person's visits across all of them.

Firefox's new option blocks only the outside kind, and in its recommended setting only for companies on a published list of trackers.

What it touches

• Remarketing audiences, the lists of past visitors your ads can follow elsewhere.
• Conversion counts that depend on an ad network spotting its own cookie again.
• Credit for ads that were seen but never clicked.
• Frequency caps, which limit how often one person sees the same ad.
• Social widgets that recognise a visitor's logged-in account.

The first is the one a small advertiser will feel. A Firefox user with the option switched on can read every page of your site without ever joining the audience your ads are built on.

What it leaves alone

Ordinary visit counts in Analytics carry on, because the cookie behind them is your own. Sessions, pages, sources and goals are recorded for Firefox users as before.

The exception is the stricter option. Somebody who blocks every known tracker in every window may stop some analytics scripts from loading altogether, since the list includes analytics companies.

That already happens in Firefox's private windows, which have blocked known trackers by default since 2015. It is a small group, and it has always been missing from the figures.

Why figures differ by browser

Every major browser now treats tracking a little differently, and the differences show up as gaps between your reports.

Safari has restricted third-party cookies for years, and tightened that again with Safari 12 in September. Firefox now offers the option above. Chrome, which most visitors use, blocks none of this by default.

Ad blockers, installed by some visitors on any browser, add gaps of their own.

So an ad platform's conversion count, the goals in Analytics and the enquiries in your inbox will never agree exactly, and the size of the gap depends on which browsers your customers use.

A worked example

A small hot springs resort in the BC Interior takes most bookings through the reservation system on its own website. It advertises with search ads and with display ads that follow past visitors around other sites.

Each autumn the manager compares bookings in the reservation system with the conversions the ad platforms report. The two have never matched, and the gap has been growing.

Analytics by browser explained much of it. Visitors on Safari, from iPhones and Macs, were a large share of the site's traffic and a much smaller share of the bookings the ad platforms claimed.

From this week, Firefox users who switch on the new option will join them.

The resort changed none of its tags. It added a question to the booking form asking how guests first heard of it.

The manager now judges campaigns on bookings in the reservation system, with the platforms' figures as a guide.

Reading Analytics by browser

Analytics can break its figures down by browser: under Audience, choose Technology, then Browser and OS, to see visits, goals and conversion rates for each.

Note this month's figures for Firefox and Safari now, before more people change their settings, so any later shift has something to be measured against.

A sudden drop in one browser's goals is not always privacy. A form that breaks in one browser after an update produces exactly the same pattern, and is worth ruling out first.

Count enquiries yourself

Every browser change this year points the same way: ad platforms will see less, and their counts will drift further from what actually happened.

The figure that does not drift is the one you keep yourself: bookings in your own system, calls answered and forms received, each with a note of where the customer came from.

Use the platforms' conversion figures to compare campaigns with each other, and your own count to decide whether the advertising pays.

What not to do

Do not try to get around the setting. Techniques for recognising browsers without cookies exist, and using them on people who have just asked not to be tracked is hard to square with any privacy policy.

Do not cut a campaign because its reported conversions dipped in one browser. Check the count you keep yourself first.

And remove the tags you no longer use. Pixels from campaigns that ended years ago still load on every page, cost speed, and add companies to your privacy policy for nothing.

The counter-case

For most small businesses, this month changes very little.

The option is off by default, Firefox is a modest share of visits on most local business sites, and its users lean towards desktops and laptops rather than phones.

A business that runs no remarketing and judges its ads by enquiries it counts itself will barely notice.

But the direction is the same in every browser, and the businesses already counting their own enquiries will be the least surprised by where it leads.

This week

1. Note Firefox and Safari figures in Analytics now.
2. Annotate the date of this change.
3. List the advertising tags on your site.
4. Remove tags from finished campaigns.
5. Ask new customers where they found you.
6. Count enquiries in your own records.
7. Compare by browser again in two months.

Step six is the one no browser can undo. A booking recorded in your own system stays counted, whatever any ad platform manages to see.

Reading small numbers without overreacting is covered in conversion rates on a site with few visitors.

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